It is known to produce aluminum in coil form from a direct casting apparatus wherein molten aluminum is cast in the form of a metal strip and rolled into a coil on a coiler. Drag casting apparatus and methods of this type are described, for example, in U.S. Pat. Nos. 4,828,012, 4,751,957, 4,896,715, and 4,934,443 and in PCT publications WO89/09667, published Oct. 10, 1989, and WO90/05604, published May 31, 1990. The disclosures of these patents and PCT publications are hereby specifically incorporated by reference with respect to the methods for the production of aluminum strip in coiled form from molten aluminum.
Generally, in this process and apparatus, metal strip is directly cast from molten metal deposited on a moving chill surface from a tundish having an open outlet. An inlet is provided for the flow of molten metal into the tundish from a source of molten metal. Diverters within the tundish divide the flow of molten metal into a plurality of separate streams and divert one of the streams in the direction of each sidewall and for recombining the diverted streams into a composite stream flowing toward the outlet. Flow diffusers diffuse the molten metal flowing through the tundish to provide molten metal of substantially uniform temperature across the width of the tundish at the outlet. The tundish is cast onto a chill wheel, preferably a grooved chill wheel, at a rapid rate.
The aluminum strip produced from this direct casting apparatus is wound on a coiler in heated form. Generally, the temperature of the aluminum on the coiler will be in the range of about 900.degree. F.
It is also known in the metal art that "as cast" material still requires refinement of grain structure or homogenization to provide a commercially acceptable product. There is substantial prior work in connection with metal stock to achieve refinement of the metal by thermal and annealing treatments. Various heat treatments have been utilized and are recognized in the aluminum art as useful to change the grain size and in effect homogenize the aluminum metal. Prior art of this type includes U.S. Pat. Nos. 4,000,008, 2,670,309, 4,028,141, 4,569,703, 4,699,673, 4,799,974, and 4,927,470. In general, these prior art patents disclose that aluminum may be treated thermally or by annealing to refine the grain structure.
None of these prior patents, however, are concerned with direct cast aluminum coils from a drag casting process.
The present invention provides a method for the refinement of aluminum metal and thus homogenization, of a coil of aluminum produced from a drag casting process.